For many years, so-called bicolour coins have been in use around the world that consist of an inner core and an outer ring surrounding the core. The core and outer ring are produced from different metal materials. It is also disclosed in DE 10 2010 013 148 to add to the coin an additional material component in the form of a central ring. The central ring which is produced, for example, from a polymer or a composite material is connected in an electrically insulating and fixed manner to the outer ring and core.
The testing of bimetal coins takes place primarily by electromagnetic measuring methods. It has been shown that due to corrosion, for example, the transition resistance between the core and the outer ring leads to errors in the measurement results. The effect of these errors is all the greater the higher the differences in potential of the metals or alloys used.
It is further disclosed in DE 10 2010 013 148 that the central ring is intended to consist of a transparent, semi-transparent, opalescent material and/or a material producing a colour effect. The width of the central ring is preferably between 0.5 mm and 3 mm.
In addition to improving the ability to test said coins by electromagnetic means, an improved capacity for differentiation relative to other conventional coins is also achieved. The user may identify, for example, a transparent central ring simply by observation.